Hi Vidya,
Please find below the script I used. It is written in a “proprietary” language but I think that you can do the same things in a perl script with calls to nco utilities (http://nco.sourceforge.net)
By this way, I converted MSLA (sea level anomalies) netCDF files (coverage: 0E - 360E / 90S - 90N) to GRASS raster ascii files (180W - 180E / 90S - 90N).
I need to be able to modify the point values of the map so as to modify the variables of the netCDF file that i shall reconvert the raster map to.
In order to do this, I think the easiest way is to use a perl or shell script to create a very simple cdf file (just one array) from the output of r.out.ascii -h. Mainly you will have to change space character with a comma.
Then you use ncgen to generate a netCDF file with just an array called SLA for example.
Then you use nco tools to replace the variable SLA in the original netCDF file (or a copy !) with the new one.
I hope that I will have some time by the end of this year to write a script to convert GRASS ascii raster file to a netCDF file…
Of course, it would be better to write a r.out.cdf and a r.in.cdf modules compiled directly against netCDF libraries but I don’t know C !
Paul
#!CDFTools
#CDFTools Cdf2AsciiPaul.oce fic_in_netcdf num_grille fic_ou_grille null_value
variables FichierCDF, Grille, Latitudes, Longitudes;
variables IndexLat, IndexLon;
variables FichierAscii, Valeur;
open grid file named argv[0] as FichierCDF for read;
read grid to_integer(argv[1]) from file FichierCDF to Grille;
Latitudes= get_latitudes(Grille);
Longitudes= get_longitudes(Grille);
open text file named argv[2] as FichierAscii for write;
write text “north: 90.00”//“\n” to file FichierAscii;
write text “south: -90.00”//“\n” to file FichierAscii;
write text “east: 180.00”//“\n” to file FichierAscii;
write text “west: -180.00”//“\n” to file FichierAscii;
write text “rows: 720”//“\n” to file FichierAscii;
write text “cols: 1440”//“\n” to file FichierAscii;
write text “null: “//to_string(argv[3])//”\n” to file FichierAscii;
write text “type: float”//“\n”//“\n” to file FichierAscii;
IndexLat= number(Latitudes)-1;
while IndexLat >= 0 do
IndexLon= 720;
while IndexLon < number(Longitudes) do
Valeur= get_element(Grille, IndexLat, IndexLon, 0);
if Valeur != DEFAULT_FLOAT then
if Valeur == DEFAULT_FLOAT then
Valeur = 9999;
end if;
write textto_string(Valeur)//" "
to file FichierAscii;
else
Valeur="9999 ";
write text Valeur to file FichierAscii;
end if;
IndexLon= IndexLon+1;
end while;
IndexLon= 0;
while IndexLon < (number(Longitudes)/2) do
Valeur= get_element(Grille, IndexLat, IndexLon, 0);
if Valeur != DEFAULT_FLOAT then
if Valeur == DEFAULT_FLOAT then
Valeur = 9999;
end if;
write textto_string(Valeur)//" "
to file FichierAscii;
else
Valeur="9999 ";
write text Valeur to file FichierAscii;
end if;
IndexLon= IndexLon+1;
end while;
IndexLat = IndexLat - 1;
write text “\n” to file FichierAscii;
end while;
At 15:40 16/12/2002 -0800, you wrote:
Hi paul,
I guess i will be comfortable with the 2nd option.
Could u pls send me the script if it is possible ?
Also, after converting the netCDF file to the raster map form,
I need to be able to modify the point values of the map so as to modify
the variables of the netCDF file that i shall reconvert the raster map to.
Like r.support is used to modify the header information how can i actually
go about modifying the variables of the netCDF by means of its
corresponding raster map ?Thanx in advance.
Vidya Kotamraju— Paul Hasenohr phasenohr@cls.fr wrote:
Hello Vidya,
I know two ways to import netCDF files into GRASS.
You install R and you use R inside GRASS. R is
able to read netCDF
files, so you can export your variable in GRASS. I
used this method six
months ago and it worked fine.An other option
You convert your netCDF file to an ascii file
readable with the r.in.ascii
command.
I prefer this option because it is less system
resources consuming.
I made a shell script to convert netCDF file into
GRASS raster ascii file
but I use netCDF tools developed by my company and
there are
not publically available. However, if you are
interested in, I can send it
to you and I believe that it is easily portable with
the nco tools
([http://nco.sourceforge.net, have a look at ncks](http://nco.sourceforge.net, have a look at ncks/))HTH
Paul
